The size of the certificate should be the international ISO size A4 (210 x 297 mm, 8.27 x 11.69 inches). The form should be provided with a 10 mm top margin and a 20 mm left-hand filing margin. Line spacing should be based on multiples of 4.24 mm (1/6 inch) and width-spacing on multiples of 2.54 mm (1/10 inch). The layout should be in conformity with the ECE layout key, as illustrated in Appendix I. Minor deviations in the exact size of boxes, etc., should be permissible if required for particular reasons in the issuing country, such as the existence of systems other than metric measurement, features of national aligned systems of documents, etc.